The single dose of vaccine given to Quebec health-care workers and long-term care residents has been 80 per cent effective at stopping COVID-19 infections, the province’s immunization committee said Thursday.
Quebec’s decision to delay vaccine booster shots past the three-to-four-week interval recommended by vaccine manufacturers has been controversial and criticized by some health experts. The province says that with a shortage of doses, the extended delay allows it to give more people a measure of protection.
The vaccine committee said that strategy has so far paid off.
And while members of the committee said results are preliminary, they recommended health officials finish giving priority groups a single dose before anyone gets a second shot of the two-dose vaccines.
“We saw that in health-care workers and in residents of long-term care facilities, the vaccine gives a protection around 80 per cent in both groups,” Dr. Gaston De Serres, epidemiologist at Quebec’s government-mandated public health institute, told reporters.
That level of protection took two weeks to develop in health-care workers and three weeks to develop in long-term care residents, who generally have weaker immune systems, he added.
Around 80 per cent of long-term care residents and 50 per cent of public sector health-care workers have received a single dose of vaccine, De Serres said, adding that since early January, the number of COVID-19 cases in long-term care homes has dropped by around 95 per cent.
Quebec began its vaccination campaign in mid-December, focusing on long-term care residents and health-care workers. It has not yet begun giving people a second shot of the two-dose vaccines.
Vaccine makers recommend the second shot be given within 21 or 28 days from the first one, depending on the vaccine. A federal committee has recommended a delay of up to 42 days. The Quebec government, however, has said it wants to give the second shot within 90 days.
De Serres said the downward trend in cases is not entirely due to the vaccination campaign. The number of cases reported in private seniors residences – where fewer people have been vaccinated – has declined by 80 per cent over the same period.
On Thursday, Quebec reported 900 new cases of COVID-19 and 10 more deaths attributed to the novel coronavirus, including four within the preceding 24 hours. Five new cases were reported in long-term care homes, while 20 new cases were reported in private seniors residences.
Hospitalizations dropped by 19, to 747, and 129 people were in intensive care, a decrease of one. Officials said 2,234 doses of vaccine were administered Wednesday, for a total of 302,118.
Dr. Nicholas Brousseau, chair of Quebec’s immunization committee, said his group is recommending Quebec give a single dose to all members of six priority groups before anyone receives a second shot. The priority groups include health-care workers, residents of long-term care and retirement homes, as well as people over 70 years old.
“That’s the way to decrease the number of hospitalizations and prevent deaths,” he said. “At the moment, we think that we have to favour a longer interval rather than a short interval to optimize the public health impact of the vaccine.”
Brousseau said the committee isn’t recommending a specific interval between injections. He said the committee’s recommendations could change if there are signs the level of protection offered by the vaccine declines over time.
Roxane Borges Da Silva, a public health professor at Universite de Montreal, said she doesn’t believe the vaccine committee’s methods – which analyzed the infection rate among people who had been vaccinated – were robust enough to draw conclusions.
There is a correlation between vaccination and a decline in the number of new cases among people who have been injected with one dose, she said. But cases have dropped across Quebec during the same period, she said, adding that without a randomized controlled trial or a robust, large-scale study, it’s impossible to determine if there’s a cause-and-effect relationship.
Dr. Sophie Zhang, who oversees 15 long-term care centres in Montreal, said the steep decline of new COVID-19 infections in long-term care homes may be an early sign Quebec’s vaccination strategy is working – but other factors are also likely contributing.
“What we’re seeing is a combination of several things in synergy and really working together to decrease the cases and mortality,” Zhang said in a recent interview. The lockdown and nighttime curfew, she added, have also contributed to the decline in the overall number of active infections in Quebec.
Joyce Shanks, a member of the Family Advocacy Committee at Maimonides, the long-term care centre where the first doses of vaccine were administered in Montreal, says she feels like the government is conducting an experiment on people who thought they would get two doses of vaccine within the time frame recommended by vaccine makers.
Her father, who lives at Maimonides, received one dose of vaccine more than 60 days ago but has not received the second. She worries the protection offered by a single dose won’t last.
“We’re holding our breath; we’re not breathing a sigh of relief,” she said Wednesday.
The Canadian Press
This story was produced with the financial assistance of the Facebook and Canadian Press News Fellowship.
Sign up for the Coronavirus Update newsletter to read the day’s essential coronavirus news, features and explainers written by Globe reporters and editors.